This invention relates generally to augmented gas turbine engine, and more particularly, to an exhaust duct flow splitter apparatus and method for controlling augmentor air flow.
Gas turbine engines generally comprise a compressor for compressing air flowing through the engine, a combustor system in which fuel is mixed with the compressed air and ignited to form a high energy gas stream, and a turbine which is connected to the compressor to drive the compressor as well as provide thrust. Airflow entering the compressor is compressed and directed to the combustor where it is mixed with fuel and ignited, producing hot combustion gases used to drive the turbine. As the performance demands of aircraft have increased, performance demands of the engines have also increased. As range demands increased, low pressure rotors were added providing higher mass flow resulting in increased thrust at better specific fuel consumption. Additionally, mission demand increases became more significant for multi-role weapon systems. For example, engines are being designed to accommodate conventional take-off and landing (CTOL) operations, as well as, short-takeoff and vertical landing (STOVL) operations. One method of increasing thrust output of a gas turbine engine is to provide the engine with an augmentor, including an exhaust duct located downstream of the turbine in which additional fuel may be injected and ignited to provide an additional high energy gas stream.
Augmentors used in aviation turbofan engines produce increased thrust by burning fuel in a separate duct downstream of the jet engine exhaust to add mass to the exhaust stream. Intense combustion induced, high frequency pressure oscillations are generated under certain operating conditions in the augmentor and are known in the art as “screech”. See, for example, U.S. Pat. No. 3,041,836, J. C. Truman et al, “Means for Eliminating Screech in Jet Propulsion Systems”, which is assigned to the present assignee. Uncontrolled screech reduces the high-cycle fatigue life of the augmentor components due to screech-induced vibration including radial, circumferential, and axial modes, and combinations thereof.
Gas turbine engine augmentors utilize cooling liners, to provide screech suppression in the augmentor, shield the structural augmentor casing from hot augmentor combustion gases and provide cooling air to an exhaust nozzle disposed at the downstream end of the augmentor. An efficient augmentor cooling liner should provide casing thermal shielding to maintain acceptable levels of metal temperature consistent with durability and life requirements for the augmentor, while utilizing the least possible amount of air for augmentor cooling.
Augmentors are generally long structures when compared to engine size and must accommodate relatively high combustion gas temperatures, both of which conditions require a substantial amount of cooling air. To improve efficiency, gas turbine engine augmentors typically utilize relatively highly effective film-cooling structures, such as are found in engine combustors. Augmentor combustion efficiency is determined by the proportional amount of discharge gases available from the gas turbine engine used for augmentor combustion. Accordingly, any engine discharge gases, for example fan bypass air utilized for cooling the augmentor liner and not used in the augmentor combustion process, decreases augmentor temperature capability and efficiency. It therefore becomes apparent that reducing the amount of air required for cooling the augmentor correspondingly increases augmentor efficiency.